1. Field of the Invention
The present invention relates to an optical module used in an optical link apparatus for data communications and the like, and a method of making the same.
2. Related Background Art
An optical module for converting an electric signal into an optical signal and sending out the latter to an optical fiber or converting an optical signal from the optical fiber into an electric signal comprises an optical device and an electronic device electrically connected to the optical device, and is widely used for optical communication systems such as data links and optical LANs employing light as an information transmitting medium.
As disclosed in Japanese Patent Application Laid-Open No. HEI 2-271308, for example, a conventional optical module is formed such that a circuit board mounted with an electronic device and an optical device assembly including an optical device are placed at predetermined positions on a lead frame, and are integrally molded with an electrically insulating resin after being electrically connected to each other by wire bonding. In such an optical module, in order to prevent the bonded wire from breaking when transporting the lead frame to a mold for resin molding in the process of manufacturing, the optical device module is held by a holding member integrally provided with the lead frame so as to keep it from shifting the position. At that time, the optical axis of the optical device in the optical device assembly is located on the lead frame surface.
The inventors studied the conventional technique mentioned above and, as a result, have found the following problems. In optical modules, positions of lead pins, positions of optical axes of optical devices, and the like are defined by industrial standards. In recent years, demands from such industrial standards have made it necessary to shift the optical axes of optical devices in optical device assemblies from the lead frame surface.
However, it is not easy for a holding member integrally provided with the lead frame as in the above-mentioned conventional optical module to reliably hold an optical device assembly at a predetermined position while in a state where the optical axis of the optical device is shifted from the lead frame surface, and quickly respond to changes in design.
Hence, it has been proposed to provide a holding member separately from the lead frame, so as to hold the optical device assembly. As a consequence, when a change occurs in the design of optical module, the holding member can be changed as needed so as to quickly respond thereto. When a holding member is provided separately from the lead frame, however, potentials of the optical device assembly, holding member, and lead frame may become unstable if conduction is insufficient between the lead frame and the holding member or between the holding member and the optical device assembly, thus deteriorating characteristics of the optical module. Therefore, conduction must fully be secured between the above-mentioned members for high-speed transmissions in particular.
In order to eliminate the problems mentioned above, it is an object of the present invention to provide an optical module which can fully secure conduction between members so as to improve their characteristics while being able to quickly respond to changes in design, and a method of making the same.
The optical module in accordance with the present invention comprises (1) an optical device assembly having an optical device for converting one of optical and electric signals into the other; (2) a circuit board for mounting an electronic device to electrically connect with the optical device; (3) a lead frame having a lead pin, a board mounting part for mounting the circuit board, and a support part which are provided on a reference surface; (4) a holding member having a holding part for grasping and holding the optical device assembly, and a grasping part for grasping the support part of the lead frame; and (5) a resin member for encapsulating the optical device assembly, the circuit board, the holding member, and the lead frame.
Since this optical module has a holding member provided separately from the lead frame, it can easily respond to changes in design of the optical module by changing the holding member as needed. The holding member has a grasping part for grasping the support part of the lead frame, and a holding part for grasping and holding the optical device assembly. Therefore, conduction is fully secured between the optical device assembly and the holding member, and between the holding member and the support part, whereby characteristics of the optical module can be improved.
Preferably, in the optical module, the grasping part of the holding member has a base portion provided so as to extend along the reference surface, and a pressing portion for urging the support part of the lead frame toward the base portion. As a consequence, the support part of the lead frame is urged toward the base portion by the pressing portion, so as to be held between the base portion and the pressing portion. This fully secures conduction between the holding member and the support part.
Preferably, in the optical module, the grasping part has a narrowest portion yielding a narrowest width between the base portion and the pressing portion, whereas the width between the base portion and pressing portion in an end portion of the grasping part on a side introduced to the support part is greater than that between the base portion and pressing portion in the narrowest portion. Preferably, an edge portion of the support part on a side where the grasping portion is introduced has a thickness smaller than that in the other portion. This makes it easier to introduce the holding member to the support part.
Preferably, in the optical module, the lead frame further comprises an auxiliary part for aiding in supporting the holding member provided on the reference surface. As a consequence, the holding member is supported more stably by the auxiliary part.
Preferably, in the optical module, the auxiliary part of the lead frame includes a positioning hole for positioning the holding member, whereas the holding member has a protrusion adapted to fit into the positioning hole. This makes it easier to position the holding member and improves the accuracy in positioning.
Preferably, in the optical module, the holding part of the holding member includes a pair of sheet spring members for holding the optical device assembly therebetween. As a consequence, the optical device assembly is held between a pair of sheet spring members, whereby conduction is fully secured therebetween.
In the optical module, the optical axis of the optical device in the optical device assembly is shifted from the reference surface. In optical modules, positions of lead pins, positions of optical axes of optical devices, and the like are defined by industrial standards, which make it necessary to shift the optical axes of optical devices in optical device assemblies from the lead frame surface. This optical module can satisfy such demands from industrial standards.
In the optical module, the optical device assembly and the circuit board are electrically connected to each other by bonding wires. In the optical module, the optical device assembly is held by the holding member while the optical device assembly and the circuit board are connected to each other by bonding wires, whereby the fear of wires breaking is reduced.
The optical module can be made by a method of making an optical module having the following steps. This method comprises (1) a step of mounting the circuit board onto the board mounting part of the lead frame; (2) a step of grasping the support part of the lead frame with the grasping part of the holding member and supporting the holding member displaceable along the reference surface; (3) a step of grasping and holding the optical device assembly with the holding part of the holding member; (4) a step of providing wire bonding between the optical device assembly and the circuit board; and (5) a step of encapsulating the optical device assembly, the circuit board, the lead frame, and the holding member with a resin.
The method of making an optical module may further comprise a step of positioning the holding member prior to the resin encapsulating step. As a consequence, the holding member can be positioned while being dislocated along the reference surface before being encapsulated with a resin, so that the positioning accuracy can be enhanced, whereby the yield and characteristics of thus produced optical module can be improved.
In the above-mentioned method of making an optical module, the grasping part of the holding member may have a base portion and a pressing portion for urging the support part of the lead frame toward the base portion, whereas the step of supporting the holding member may include a step of engaging an edge portion of the support part between the base portion and the pressing portion, and a step of pushing the holding member toward the support part. As a consequence, a position for supporting the holding member can approximately be determined by engaging the edge portion of the support part between the base portion and the pressing portion, and the holding member is supported by the support part when the holding member is pushed toward the support part.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings. They are given by way of illustration only, and thus should not be considered limitative of the present invention.